Obama apologises over Koran burning

President Barack Obama was forced to apologise over the burning of Korans at a US airbase in Afghanistan, where three days of violent protests have killed 14 people, including two American soldiers.

Kabul was bracing Friday for further anti-US demonstrations that have seen furious Afghans attack French, Norwegian and US bases after the Taliban exhorted their countrymen to kill foreign troops to avenge the incident.

Afghanistan is a deeply religious country where slights against Islam have frequently provoked violent protests, and many Afghans are incensed at the discovery of charred Korans at Bagram airbase north of Kabul.

In a letter to Afghan President Hamid Karzai, Obama Thursday expressed "deep regret" over the incident that he said had been unintentional, and pledged that those responsible would be held accountable, Kabul said.

"I extend to you and the Afghan people my sincere apologies," Obama wrote in the letter presented to Karzai by US ambassador Ryan Crocker.

"The error was inadvertent; I assure you that we will take the appropriate steps to avoid any recurrence, to include holding accountable those responsible."

Karzai said a US officer was responsible -- "out of ignorance" -- for the Koran burning, the president's office said.

Obama's apology came in for strong criticism back home, with partisan politics playing a part as competition builds in a presidential election year.

"It is an outrage that President Obama is the one apologising to Afghan President Karzai on the same day two American troops were murdered and four others injured by an Afghan soldier," Republican presidential hopeful Newt Gingrich said.

"It is Hamid Karzai who owes the American people an apology, not the other way around."

But White House spokesman Jay Carney said the apology, which came in a broader three-page letter to Karzai, "was absolutely the right thing to do".

"His primary concern as commander in chief is the safety of American men and women in Afghanistan, of our military and civilian personnel there," Carney said.

The two Americans were shot dead by an Afghan soldier at their base in Khogyani in eastern Nangarhar province, district governor Mohammad Hassan told AFP.

At least three Afghans were also killed by gunfire at demonstrations in the south and east of the country, bringing the total death toll among protesters to 12 since Wednesday.

The US embassy warned of further possibly violent protests Friday in which Westerners could be targeted.

The "emergency message" urged Americans in Afghanistan to "shelter in place and avoid any unnecessary movement", with at least one demonstration reportedly planned for Kabul and more possible after Friday prayers.

"Road closures are expected and it is possible the protests will become violent," it said.

The violence came after the Taliban urged Afghans to kill foreign troops to avenge the Koran burning, although the insurgents stopped short of cutting off tentative peace contacts with US officials in Qatar.

In Mihtarlam, the capital of Laghman province east of Kabul, thousands besieged the base of a US-led military-civilian provincial reconstruction team (PRT), throwing rocks and climbing up the outer walls, police said.

"People had come from all over Laghman. They attacked the PRT, they climbed up the walls, they set fire to something there, I think a container," police official Khalilul Rahman Niazi told AFP.

About 2,000 protesters also tried to march on the French base in Kapisa, east of Kabul, but were pushed back by Afghan security forces, regional police chief General Abdul Hameed Erken told AFP.

Karzai had called for calm pending a full investigation, and ordered his own security forces to avoid violence and protect lives and property.

But the Taliban, leading a 10-year insurgency against Karzai's government, sought to exploit the anti-American sentiment.

"You should bring the invading forces' military bases under your brave attack, their military convoys, kill them, capture them, beat them and teach them a lesson that they will never again dare to insult the Holy Koran," they said in a statement.

The Islamist movement was toppled in the 2001 US-led invasion. NATO has some 130,000 troops, mainly Americans, supporting the Karzai government.

US officials speaking on condition of anonymity told AFP the military removed Korans from a prison at Bagram because inmates were suspected of using the holy book to pass messages to each other.